1. Field of the Invention
The present invention relates to a mask for sequential lateral solidification and a method of performing sequential lateral solidification using the same. More specifically, the present invention relates to a mask that may be used for sequential lateral solidification and a method of performing sequential lateral solidification using the same. The method may result in a material in which crystal defects are reduced or eliminated, and which can induce the growth of larger crystal grains.
2. Description of the Related Art
Among crystallization techniques for transforming amorphous silicon into polysilicon, sequential lateral solidification (SLS) is an important technique. SLS may be used for fabricating a high performance thin film transistors, due to its ability to obtain larger silicon grains, compared with the other crystallization techniques. According to such a sequential lateral solidification technique, a laser beam passes through a mask formed with a slit, to crystallize amorphous silicon. That is, if the amorphous silicon is irradiated by the laser through the mask slit, the amorphous silicon irradiated with the laser beam is completely melted and then solidified, resulting in crystal growth. During solidification, the crystal grains grow from both edges (of the region on which the laser beam is irradiated) laterally toward the center of the amorphous silicon, and the growth stops at a central portion where the grains meet each other.
FIG. 1A is a schematic plan view of a conventional mask for sequential lateral solidification. Referring to FIG. 1A, the mask 5 is composed of a first slit column 3 which includes a plurality of first slits 1 arranged at regular intervals, and a second slit column 4 which includes a plurality of second slits 2 arranged at regular intervals, and which is disposed adjacent to and offset from the first slit column 3. FIG. 1B shows the intensity distribution of a laser beam transmitted through the mask of FIG. 1A. Each of the first and second slits 1 and 2 is a transmission region where the laser beam is completely transmitted, whereas the remaining area is a non-transmission region where the laser beam is not transmitted. FIG. 1C shows a simulation of polysilicon grains grown using a mask such as mask 5 of FIG. 1A.
FIG. 2A schematically illustrates a scanning pattern according to stage movement of a sequential lateral solidification apparatus, and FIG. 2B is a photograph showing a conventional polysilicon thin film in which a line-overlap defect occurred.
Referring to FIG. 2A, a stage on which a substrate is placed causes a shot-to-shot offset in a scanning direction depending on the speed at which the stage moves. Shot-to-shot offset is generally caused by a combination of rolling, pitching, yawing and optical abnormality, which in turn are caused by properties inherent to the stage, when the stage moves straight. If such a shot-to-shot offset occurs, the size of overlap between lines where the laser beam transmits and crystal growth occurs may be changed. In a case such as that shown in FIG. 1C, where the spacing between the lines is large, a line-overlap defect may occur, as shown in FIG. 2B. As a result, degradation occurs in the area where the overlap defect is produced, which can lead to a defective pixel and thus to a defective image.